The disclosure relates generally to operation and design of monolithic reactors, and more particularly to methods of operating and designing monolithic reactors which may be used in exhaust gas after-treatment devices.
No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinence of any cited documents.
Monolithic reactors in the form of honeycomb substrates incorporating catalytically active materials have been used to treat and clean exhaust gasses from automobile and truck engines for many years. Exemplary after-treatment devices for emissions control include three-way catalysts (TWC) which remove carbon monoxide (CO), hydrocarbons (HC) and nitrous oxides (NOx) from exhaust gasses. Other exemplary devices for emission control include systems that utilize selective catalytic reduction (SCR) of NOx, and diesel oxidation catalysts (DOC).
Modern exhaust gas after-treatment devices are very efficient and convert emissions to benign gases with almost 100% efficiency at high temperatures. Most of the tailpipe emissions which are not converted occur during the “cold-start” period (i.e., the first few tens of seconds during which the substrate and catalyst(s) incorporated on and/or in the substrate heat up from ambient temperature). At these low temperatures, the performance of the catalyst is limited due to reaction and mass transfer limitations.
It is accordingly important to reduce the time required to heat the after-treatment device (i.e., the substrate and catalyst(s) incorporated on and/or in the substrate) to a temperature at which polluting species are converted into benign products.